This invention concerns improvements in and relating to lightweight aggregate, more particularly lightweight aggregate which may be employed in the making of concrete. This invention in particular relates to the loose particulate material in various gradings of size which can be mixed with cement for the making of concrete.
Lightweight aggregate (abbreviated LWA) is an important material for prefabricated concrete construction techniques. Normal prefabricated concrete components cause considerable problems and costs in their transportation to the site and in their installation on site. The reason for this is that these components easily become very heavy due to the high density of conventional concrete. A further disadvantage of conventional concrete prefabricated components is that they can break under their own weight during handling particularly for example when they are incorrectly lifted. These problems can be overcome to a large extent by the use of lightweight concrete and such material has gained appreciable acceptance in the art. The use of LWA for prefabricated concrete components results in lighter components with substantial reductions in transportation and handling costs and in some cases lessened tendency for breakages. These advantages are, however, in many cases detracted from by the disadvantage of relatively high manufacturing cost of LWA as compared with ordinary quarried stone. The LWA which is generally available is manufactured in high temperature rotary kilns or blast furnaces. These manufacturing techniques inevitably result in rather high costs being incurred, particularly high capital costs and high heating costs. Particularly in a relatively low volume turnover, this causes the LWA to be expensive.
Included in these types of LWA are those produced from clays, shale, slag or cinders which are expanded at high temperature to produce a porous rock-like substance which may either be produced immediately in the final sizes and then graded or which may be ground into desired sizes.
The compressive strength of these units may even be made comparable with quarried stone in the best examples. LWA has further advantages apart from its low weight, including better heat and sound insulating qualities and also water absorption qualities which is beneficial for obtaining a fast initial set of the concrete in use.
LWA is generally classified in terms of size into so called coarse aggregate and fine aggregate, the arbitrary division being 1/4" and above being classified as coarse aggregate and 3/16" and below being classified as fine aggregate. Concrete can be manufactured entirely from LWA and cement or else either of the coarse aggregate or the fine aggregate can be natural stone while the other is LWA.